The Gilder Lehrman Institute of American History Advanced Placement United States History Study Guide

September 11, 2001

“9/11” has emerged as shorthand for the four coordinated terrorist attacks on the United States that took place on September 11, 2001. That morning, nineteen terrorists from the Islamist extremist group al Qaeda hijacked four commercial airplanes, deliberately crashing two of the aircraft into the upper floors of the 110-story North and South Towers of the World Trade Center (WTC) complex in New York City and a third plane into the Pentagon in Arlington, Virginia. After learning about the other attacks, passengers and crew members on the fourth hijacked jet, Flight 93, launched a counterattack, which foiled the plot but resulted in the plane’s intentional crash into an empty strip mine field in western Pennsylvania roughly twenty minutes by air from Washington, DC. The attacks ultimately claimed 2,977 victims, the single largest loss of life resulting from a foreign attack on American soil.

The four westbound flights—American Airlines Flight 11, United Airlines Flight 175, American Airlines Flight 77, and United Airlines Flight 93—departed from airports in Boston, Massachusetts; Newark, New Jersey; and Washington, DC. In addition to sharing coordinated departure times, all were carrying large amounts of jet fuel for their crosscountry trips to California. Both factors were calculated choices by the terrorists to inflict maximum damage to their targets. The weather on September 11 facilitated the plot, dawning with a cloudless blue sky.

Hijacked Flight 11, with 87 passengers and crew aboard, struck the North Tower at 8:46 a.m. between the 93rd and 99th floors. The impact instantly killed hundreds of people, creating a huge gash in the north side of the tower. The plane also severed all three stairwells, destroying the escape routes for everyone working at or above the impact zone.

As the world focused its attention on the unfolding disaster, most assumed the event was an accident. However, seventeen minutes later, at 9:03 a.m., hijacked Flight 175 struck the south side of the South Tower between the 77th and 85th floors. The plane had 60 passengers and crew aboard. The impact, caught on television and seen live or in broadcast replays around the world, confirmed that the country was under attack. Unlike the North Tower, one stairwell remained passable in the South Tower, allowing eighteen people at or above the impact zone to escape to safety.

When the buildings were struck, an estimated 16,400 to 18,000 people were at work or passing through the WTC, a seven-building, 16-acre complex in lower Manhattan. Of those, the vast majority managed to evacuate safely. As they rushed out, first responders—members of the New York City Fire Department (FDNY), New York City Police Department (NYPD), Port Authority Police Department (PAPD), and other rescue agencies—rushed in, trying to save those trapped or injured inside. In total, more than 200 fire units, 2,200 police officers, and numerous others from city and federal agencies responded to the attacks.

Firefighters, many burdened by approximately 100 pounds of gear, headed upstairs to assist the injured, free trapped civilians, and fight the fires raging above. Unknown to everyone, the buildings were nearing collapse. Both towers had sustained extensive damage to the outer façade and inner core columns that together supported each building. Many columns were damaged; some had been severed. At the same time, fires burned on multiple floors. With fireproofing blown off by the force of the planes’ impacts, the steel began to weaken as it heated to roughly 1,100 degrees Celsius. As the weakened steel floor plates and trusses lost strength, they began to sag, pulling in on the damaged outer columns, causing them to bow and ultimately buckle. After burning for fifty-six minutes, the South Tower began its cascading collapse at 9:59 a.m. The North Tower stood for a total of 102 minutes before meeting the same catastrophic fate at 10:28 a.m.

As events unfolded at the World Trade Center, the other hijacked flights progressed toward their targets. At 9:37 a.m., hijacked Flight 77 crashed into the western face of the Pentagon in Arlington, Virginia, with fifty-nine passengers and crew on board, killing 125 inside the building. A segment of the Pentagon’s E-Ring collapsed at 10:15 a.m., although no rescue workers were injured.

Local air traffic delayed the take-off of Flight 93 for approximately twenty-five minutes at Newark International Airport. This delay ultimately allowed its forty passengers and crew to learn about the attack at the World Trade Center from calls placed to family and authorities on the ground. Collectively, the passengers mounted a counterattack, causing the hijacker pilots to deliberately crash the plane. At 10:03 a.m., hijacked Flight 93 tunneled into a vacant field in Somerset County just outside of Shanksville, Pennsylvania. Authorities believe the flight was headed toward the United States Capitol, about twenty minutes away.

The attacks killed 2,977 people from more than ninety countries and territories. The oldest victimwas eighty-five; the youngest was two. Included in this toll are 441 first responders, marking this event as the greatest single loss of rescue personnel in American history.

The targets of the attack were purposefully chosen by al Qaeda, an international Islamist extremist terrorist network founded by Osama bin Laden and others in the late 1980s. “Islamists” believe that strict adherence to Islamic religious law should be the sole basis for a country’s laws, as well as its cultural and social life. “Islamist extremists” are willing to use violence to achieve these ends. Historically, al Qaeda has sought to overthrow governments in the Middle East, and elsewhere in the Muslim world, that do not enforce this specific worldview. Over time, the organization’s focus shifted to the United States, seeing the US as the primary supporter of the governments it hoped to replace.

Lacking the military capacity to destroy the United States, al Qaeda set its sights on symbolic targets instead. The World Trade Center symbolized globalization and America’s economic power and prosperity. The Pentagon, as the headquarters for the US Department of Defense, serves as a symbol of American military power. The United States Capitol is the hub of the American system of democratic government. Al Qaeda hoped that by attacking these symbols, they would promote widespread fear throughout the country and severely weaken America’s standing worldwide.

The attacks’ repercussions are still being felt today. In October 2001, the United States invaded Afghanistan, whose Islamist government had harbored al Qaeda before the attacks. American troops remain there today. The Patriot Act, controversial and expansive legislation designed to provide government agencies with the tools to combat terrorism, was passed into law in late October 2001. Congress also created the Victims’ Compensation Fund, which provided support to victims’ families. Government investigations, summarized in the 9/11 Commission Report and the National Institute of Standards and Technology’s (NIST) Final Report on the Collapse of the Towers, explained what had happened and why, and made recommendations for policies that would reduce American vulnerability to future attacks. Osama bin Laden was killed in a US military raid in Pakistan on May 1, 2011. Questions of how to balance civil liberties and national security, how to detain and prosecute al Qaeda members, and how to memorialize and make meaning of such a horrific event are still being debated.

The attacks of 9/11 demonstrated the harm that humanity is capable of inflicting. But it was also a time when countless compassionate and heroic deeds occurred in the face of almost unimaginable adversity. The shock and the sadness experienced by the public in the wake of September 11 also brought people of diverse backgrounds and worldviews together in a way that engendered deep feelings of solidarity. Ultimately, the murderous actions by a few were met with continuing acts of selflessness by many. The ongoing legacy of 9/11 begins here.

The National September 11 Memorial & Museum serves as the country’s principal institution for examining the implications of the events of 9/11, documenting the impact of those events, and exploring the continuing significance of September 11, 2001.